Modulation Division Multiple Access

ABSTRACT

The present invention employs hierarchical modulation to simultaneously transmit information on different modulation layers using a carrier RF signal. Initially, first data to be transmitted is assigned to a first modulation layer and second data is assigned to a second modulation layer. In one embodiment of the present invention, the first and second data are assigned based on reliability criteria. The first and second modulation layers are hierarchical modulation layers of the carrier RF signal. Once assigned, the first data is transmitted using the first modulation layer of the carrier RF signal and the second data is transmitted using the second modulation layer of the carrier RF signal. In one embodiment of the present invention, information may be transmitted to one end user using one modulation layer, and information may be transmitted to a different end user using a different modulation layer.

RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 13/349,169, filed Jan. 12, 2012, which is acontinuation of U.S. patent application Ser. No. 11/942,492, filed Nov.19, 2007, which claims the benefit of U.S. provisional patentapplication Ser. No. 60/882,921, filed Dec. 30, 2006, the disclosures ofwhich are hereby incorporated by reference in their entireties.

This application is also related to U.S. patent application Ser. No.11/618,774 entitled CONTENT DIFFERENTIATED HIERARCHICAL MODULATION USEDIN RADIO FREQUENCY COMMUNICATIONS by Steer et al, filed Dec. 30, 2006,which is hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to radio frequency (RF) transmittermodulation techniques used in RF communications systems.

BACKGROUND OF THE INVENTION

With each successive generation of RF communications systems, modulationtechniques, access schemes, and communications protocols become moresophisticated and demanding. One universal goal is to increase theamount of information transmitted in a given communications band, and toaccommodate different types of information that must be communicated.For example, first generation cellular networks were designed to provideonly voice services; however, these networks have evolved to provide anumber of simultaneous services, including internet traffic, such asemails, and provide multi-media services, such as broadcast and ondemand services in specific geographic areas. Each of these services mayhave its own specific requirements for bandwidth, latency, acceptableerror rate, and locations of availability. As a result, differentprocessing methods have been developed, including orthogonal frequencydivision multiplexing (OFDM), single carrier frequency divisionmultiplexing (SC-FDM), single frequency networks (SFN), multiple inputmultiple output (MIMO), and multi-hop and relayed transmissions. OFDMand SC-FDM can distribute a high bandwidth signal onto multiplesub-carriers of lower bandwidth. SFNs improve signal coverage ofbroadcast data by transmitting the same information at the same timefrom multiple antennas. MIMO adds antennas to a system to providespatial multiplexing, diversity, or both. Multi-hop and relayedtransmissions provide broadcast data to multiple base stations.Therefore, as communications systems evolve, there is a need to increasethe number and diversity of services by improving how bandwidth isutilized.

SUMMARY OF THE INVENTION

The present invention employs hierarchical modulation to simultaneouslytransmit information on different modulation layers using a carrier RFsignal. Initially, first data to be transmitted is assigned to a firstmodulation layer and second data is assigned to a second modulationlayer. In one embodiment of the present invention, the first and seconddata are assigned based on reliability criteria. The first and secondmodulation layers are hierarchical modulation layers of the carrier RFsignal. Once assigned, the first data is transmitted using the firstmodulation layer of the carrier RF signal and the second data istransmitted using the second modulation layer of the carrier RF signal.One modulation layer is generally a higher order than the othermodulation layer. In one embodiment of the present invention,information may be transmitted to one end user using one modulationlayer, and information may be transmitted to a different end user usinga different modulation layer.

All things being equal, the lower order modulation layer is generallymore reliable than the higher order modulation layer. In general, thereliability criteria takes the reliability characteristics of thedifferent modulation layers into account when assigning the first andsecond data to the different modulation layers. For example, reliabilityinformation may be derived from signal strength measurements or channelconditions to determine an appropriate modulation to use fortransmitting certain data. Alternatively, different data may beassociated with different transmission priorities. Entertainmentchannels may have a lower priority than emergency service channels.Although maintaining data integrity is important for file transfers, therelative transmission priority for a file transfer is generally muchlower than that for voice or other streaming media. In essence, thereliability criteria may relate to the communication channels, thetransmission of the data, or both. An example of reliability criteriarelated to transmission of the data is data that cannot bere-transmitted requires higher reliability than data that can bere-transmitted. For the various data, the reliability information isused to assign the various data to the different modulation layers fortransmission.

In certain embodiments of the present invention, different data isbroadcast to multiple users using different modulation layers. Thedifferent data may be assigned to specific modulation layers based onreliability criteria. In one embodiment of the present invention, asingle program is broken into two different data streams.

In voice applications, each modulation layer may support one or morevoice calls. As such, the reliability criteria may be used whenassigning data for different voice calls to the different modulationlayers. Some calls are supported on higher order modulation layers whileothers are supported on lower order modulation layers in light of thereliability criteria.

Those skilled in the art will appreciate the scope of the presentinvention and realize additional aspects thereof after reading thefollowing detailed description of the preferred embodiments inassociation with the accompanying drawing figures.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

The accompanying drawing figures incorporated in and forming a part ofthis specification illustrate several aspects of the invention, andtogether with the description serve to explain the principles of theinvention.

FIG. 1 shows an RF communications system.

FIG. 2A shows a modulation symbol having 4 bits of information.

FIG. 2B shows one embodiment of the present invention wherein themodulation symbol illustrated in FIG. 2A is divided into a lowermodulation sub-symbol and a higher modulation sub-symbol.

FIG. 2C shows a modulation symbol having 6 bits of information.

FIG. 2D shows one embodiment of the present invention wherein themodulation symbol illustrated in FIG. 2C is divided into a lowermodulation sub-symbol, a middle modulation sub-symbol, and a highermodulation sub-symbol.

FIG. 3 shows the present invention used with quadrature modulation.

FIG. 4 shows the four constellation points used in quadrature phaseshift keying (QPSK) modulation, and their relationship with the lowermodulation sub-symbol.

FIG. 5 shows the 16 constellation points used in rectangular sixteenquadrature amplitude modulation (16-QAM), and their relationship withthe lower modulation sub-symbol.

FIG. 6 shows the 4 constellation points used in the first quadrant of16-QAM.

FIG. 7A shows the alignment of lower modulation layer data with highermodulation layer data in one embodiment of the present invention.

FIG. 7B shows the lower modulation layer data time-shifted from thehigher modulation layer data in an alternate embodiment of the presentinvention.

FIG. 8A shows time multiplexed data included in the higher modulationlayer data.

FIG. 8B shows two single-frequency OFDM sub-carriers included in thehigher modulation layer data.

FIG. 9 adds MIMO antennas to the base stations and some of the terminalsillustrated in FIG. 1.

FIG. 10 shows single input single output (SISO) data included in thelower modulation layer data, and two MIMO sub-channels included in thehigher modulation layer data.

FIG. 11 shows the present invention used with MIMO transmittercircuitry.

FIG. 12 shows details of the first base station illustrated in FIG. 1.

FIG. 13 is a block representation of a cellular communication system.

FIG. 14 is a block representation of a base station according to oneembodiment of the present invention.

FIG. 15 is a block representation of a mobile terminal according to oneembodiment of the present invention.

FIG. 16 is a logical breakdown of an OFDM transmitter architectureaccording to one embodiment of the present invention.

FIG. 17 is a logical breakdown of an OFDM receiver architectureaccording to one embodiment of the present invention.

FIG. 18 illustrates a pattern of sub-carriers for carrying pilot symbolsin an OFDM environment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The embodiments set forth below represent the necessary information toenable those skilled in the art to practice the invention and illustratethe best mode of practicing the invention. Upon reading the followingdescription in light of the accompanying drawing figures, those skilledin the art will understand the concepts of the invention and willrecognize applications of these concepts not particularly addressedherein. It should be understood that these concepts and applicationsfall within the scope of the disclosure and the accompanying claims.

The present invention employs hierarchical modulation to simultaneouslytransmit data over different modulation layers using a carrier RFsignal. Each modulation layer may be of a higher or lower order than theother modulation layers. Certain embodiments of the present inventionmay transmit different information on the different modulation layers.Other embodiments of the present invention may use the different layersfor processing different information streams.

Transmitting different information on different modulation layers mayprovide many useful applications. Unicast data is transmitted to asingle user, whereas broadcast data is transmitted to multiple users.The present invention includes any combination of unicast data andbroadcast data to be transmitted using any combination of the differentmodulation layers. Unicast data and broadcast data include differenttypes of content, including audio content, video content, voice content,and specific data content.

Audio content may provide at least one channel of audio programming,which may provide an on demand audio program that is unicast to a singleuser, or distributed audio programs that are broadcast to multipleusers. Similarly, video content may provide at least one channel ofvideo programming. Voice content may include individual cellulartelephone calls. Specific data content may include internet data,including emails, short messaging service messages, or downloadedinformation. The present invention includes any combination of types ofcontent to be transmitted using any combination of the differentmodulation layers.

In the present invention, the different information on differentmodulation layers may be transmitted to different geographic areas. Thecontent of the different information may be associated with differentgeographic areas. One example is a national news program may bebroadcast to a large geographic area from multiple communicationinterfaces, such as base stations, using one modulation layer, and alocal traffic program may be broadcast to a subset of the largegeographic area from one communications interface, such as a basestation, using a different modulation layer.

The present invention may include using the different modulation layersin conjunction with other techniques for processing differentinformation streams. One modulation layer may be used to providebroadcast data to multiple base stations that form a single frequencynetwork (SFN). A SFN may be used to improve signal coverage of broadcastdata by transmitting the same information at the same time from multipleantennas.

MIMO adds antennas to a system to provide spatial multiplexing,diversity, or both. The information transmitted from MIMO antennas maybe provided from any combination of the different modulation layers. Theadditional MIMO antennas may be used to strengthen a SFN. One modulationlayer may be used to provide broadcast data, which is transmitted frommultiple MIMO antennas simultaneously. Another modulation layer may beused to provide multiple channels of data, which are transmitted fromdifferent MIMO antennas.

Video broadcast data may have high bandwidth requirements. OFDM orSC-FDM can distribute a high bandwidth signal onto multiple sub-carriersof lower bandwidth. The present invention may be used to provide atleast one sub-carrier using one modulation layer, and other informationusing at least one other modulation layer.

Multi-hop and relayed transmissions provide broadcast data or othersystem data to multiple base stations. The present invention may be usedto provide any combination of system data, relayed data, and end userdata using any combination of modulation layers. Certain modulationtechniques may include one or more modulation layers that are compatiblewith modulation techniques that are used in existing communicationsnetworks. Therefore, the present invention may provide compatibilitybetween different communications systems by using compatible modulationlayers, which may allow an upgraded communications system to be backwardcompatible with a legacy user element (UE).

The present invention may be used to simultaneously download informationdirectly to a user element (UE) and to transmit system information tosystem transceivers, such as communications interfaces, which mayinclude base stations, cellular phone base stations, repeaters, relays,access points, or the like. The system information may includeinformation for downloading by other system transceivers andsynchronization information for broadcasting user information frommultiple transceivers and antennas simultaneously. The present inventionmay provide compatibility between different communications systemshaving different modulation schemes, which may allow an upgradedcommunications system to be backward compatible with legacy UE.Additionally, low cost UE using the legacy modulation scheme could befeasible with such a system. For example, an upgraded system usingmultiple antennas, such as MIMO may be compatible with systems usingsingle antennas, such as single input single output (SISO). A basicbroadcast channel may be transmitted using one modulation layer from allof the MIMO antennas, and multiple supplemental broadcast channels maybe transmitted using another modulation layer from different MIMOantennas. Legacy UE may receive the basic broadcast channel; however,upgraded UE is required to receive the supplemental broadcast channels.

Multiplexing is a processing technique for transmitting differentstreams of information using a common transmission entity. Frequencydivision multiplexing (FDM) transmits different streams of informationusing different frequencies. Time division multiplexing (TDM)interleaves different streams of information into a single combinedinformation stream, which is then transmitted. Orthogonal frequencydivision multiplexing (OFDM) and single carrier frequency divisionmultiplexing (SC-FDM) may combine FDM and TDM to create multiplesub-carriers for transmitting different streams of information. Othermultiplexing techniques may be used with OFDM and SC-FDM to provideadditional sub-carriers. Multiple input multiple output (MIMO) is amultiple antenna architecture, which may provide spatial multiplexing byallowing different information to be transmitted using differentantennas. The present invention is associated with a new multiplexingtechnique called modulation division multiplexing (MDM), by transmittingdifferent information on different modulation layers. MDM may beassociated with a new multiple access technique called modulationdivision multiple access (MDMA). The present invention may be used witha single carrier RF signal, a multiple carrier RF signal, or both. Anyfrequency or bandwidth RF signal may be used with the present invention.In one embodiment of the present invention, information may betransmitted to one end user using one modulation layer, and informationmay be transmitted to a different end user using a different modulationlayer.

An existing user element may be able to receive and transmit only thelower modulation layer, and ignore the higher modulation layer. Anupgraded system may be backward compatible with existing communicationsequipment using existing features, while adding additional features thatmay be supported with upgraded equipment. In one embodiment of thepresent invention, the hierarchical modulation method includesrectangular quadrature amplitude modulation (QAM), where lower layermodulation layer bits are encoded with only phase shifting, such as dataused with quadrature phase shift keying (QPSK), and upper modulationlayer bits are encoded with QAM; however, existing communicationsequipment may ignore the QAM data bits and receive only those bitsencoded with quadrature phase shift keying.

FIG. 1 shows an RF communications system 10, such as a cellularcommunications system, having a first base station 12 with a firstantenna port ANT1 coupled to a first base station antenna 14, a secondbase station 16 with the first antenna port ANT1 coupled to a secondbase station antenna 18, a first mobile terminal 20 with the firstantenna port ANT1 coupled to a first mobile antenna 22, a fixed terminal24 with the first antenna port ANT1 coupled to a fixed terminal antenna26, a second mobile terminal 28 with the first antenna port ANT1 coupledto a second mobile antenna 30, and a third mobile terminal 32 with thefirst antenna port ANT1 coupled to a third mobile antenna 34. Theantennas 14, 18, 22, 26, 30, 34 transmit and receive radiated RF signals36. The base stations 12, 16 control information flow to and from theterminals 20, 24, 28, 32, which ideally are controlled by whichever basestation is the closest, presents the best quality RF link, or both.

The radiated RF signals 36 are modulated to encode digital information.A number of modulation and encoding techniques may be used, includingfrequency modulation (FM) with frequency shift keying (FSK), phasemodulation (PM) with phase shift keying (PSK), amplitude modulation (AM)with amplitude shift keying (ASK), or any combination thereof. Onecommon modulation technique in cellular communications systems is acombination of AM and PM, which is called quadrature amplitudemodulation (QAM). One common modulation technique in early generationsof cellular communications systems is quadrature phase shift keying(QPSK), which can encode 2 bits of information with each modulationsymbol, or phase shift. FIG. 2A shows a modulation symbol 38 having 4bits of information, including bit zero 40, bit one 42, bit two 44, andbit three 46. To encode 4 bits of information, 16 different possiblemodulation points are required for each modulation symbol 38.

FIG. 2B shows one embodiment of the present invention by dividing themodulation symbol 38 illustrated in FIG. 2A into a lower modulationsub-symbol 48 and a higher modulation sub-symbol 50. The lowermodulation sub-symbol 48 includes bit two 44 and bit three 46. Thehigher modulation sub-symbol 50 includes bit zero 40 and bit one 42. Thelower and higher modulation sub-symbols 48, 50 may encode informationthat is unrelated, that may be on different channels or sub-channels, orthat may be differentiated in some manner.

FIG. 2C shows a modulation symbol 52 having 6 bits of information,including bit zero 40, bit one 42, bit two 44, bit three 46, bit four54, and bit five 56. To encode 6 bits of information, 64 differentpossible modulation points are required for each modulation symbol 52.FIG. 2D shows one embodiment of the present invention by dividing themodulation symbol 52 illustrated in FIG. 2C into a lower modulationsub-symbol 48, a middle modulation sub-symbol 58, and a highermodulation sub-symbol 50. The lower modulation sub-symbol 48 includesbit four 54 and bit five 56. The middle modulation sub-symbol 58includes bit two 44 and bit three 46. The higher modulation sub-symbol50 includes bit zero 40 and bit one 42. The lower, middle, and highermodulation sub-symbols 48, 58, 50 may encode information that isunrelated, that may be on different channels or sub-channels, or thatmay be differentiated in some manner. Other embodiments of the presentinvention may divide the modulation symbol 52 into more than threehierarchical modulation sub-symbols, such as the lower modulationsub-symbol 48, the middle modulation sub-symbol 58, the highermodulation sub-symbol 50, and at least one supplemental modulationsub-symbol.

The present invention may use a modulation symbol, which may be dividedinto any number of sub-symbols. Each sub-symbol may include any numberof bits. Each bit of data in a modulation sub-symbol may be used totransmit data intended for one unique receiver only or for more than onereceiver. Multiple bits of data in a modulation sub-symbol may be usedto transmit data intended for one unique receiver only or for more thanone receiver. Any receiver that receives transmitted data may receiveall or part of a modulation symbol. The receiver may process all or partof a modulation symbol. The receiver may receive one or moresub-symbols. The receiver may process one or more sub-symbols. Thereceiver may receive one or more bits in a sub-symbol. The receiver mayprocess one or more bits in a sub-symbol. For example, bit zero 40 maybe used to transmit data to a first receiver, bit one 42 may be used totransmit data to a second receiver, bit two 44 may be used to transmitdata to a third receiver, bit three 46 may be used to transmit data to afourth receiver, bit four 54 may be used to transmit data to a fifthreceiver, and bit five 56 may be used to transmit data to a sixthreceiver. Alternatively, bit zero 40 may be used to transmit data to afirst receiver, bit one 42 may be used to transmit data to a secondreceiver, bits two and three 44, 46 may be used to transmit data to athird receiver, and bits four and five 54, 56 may be used to transmitdata to a plurality of receivers.

FIG. 3 shows one embodiment of the present invention used withquadrature modulation 60, which is associated with phase modulation.Phase-shifts may be represented graphically on a two dimensional gridhaving an in-phase axis and a quadrature-phase axis. The two dimensionalgrid may be divided into four quadrants, including a first quadrant 62,a second quadrant 64, a third quadrant 66, and a fourth quadrant 68. Ifthe four quadrants are used to represent four different possiblemodulation points, then two bits of information can be encoded, whichcould correspond with bits two and three 44, 46 of the lower modulationsub-symbol 48. The first quadrant 62 may be represented with bit two 44equal to a zero and bit three 46 equal to a zero. The second quadrant 64may be represented with bit two 44 equal to a one and bit three 46 equalto a zero. The third quadrant 66 may be represented with bit two 44equal to a zero and bit three 46 equal to a one. The fourth quadrant 68may be represented with bit two 44 equal to a one and bit three 46 equalto a one.

FIG. 4 shows the four constellation points used in quadrature phaseshift keying (QPSK) modulation, and their relationship with the lowermodulation sub-symbol 48, including bits two and three 44, 46. The fourconstellation points include a first quadrant point 70, a secondquadrant point 72, a third quadrant point 74, and a fourth quadrantpoint 76. The four constellation points used in QPSK have equalamplitudes and are differentiated only by phase; however, as long as theconstellation points fall within the correct quadrant 62, 64, 66, 68,the lower modulation sub-symbol 48, including bits two and three 44, 46will be decoded correctly. This characteristic may be beneficial inmixing a system with phase and amplitude modulation, such as QAM, with asystem having only phase modulation, such as QPSK. The QPSK system maybe able to reliably receive and transmit the lower modulation sub-symbol48 in systems with QAM; therefore, upgraded communications equipmentusing QAM may be backward compatible with existing communicationsequipment using QPSK for certain features. In one embodiment of thepresent invention, a communications system may alternate betweentransmitting QAM signals and QPSK signals. Other embodiments of thepresent invention may use other combinations of FM, PM, and AM toprovide hierarchical modulation systems. Some embodiments of suchsystems may be backward compatible.

FIG. 5 shows the 16 constellation points used in rectangular sixteenquadrature amplitude modulation (16-QAM), and their relationship withthe lower modulation sub-symbol 48. With 16 different possiblemodulation points, then 4 bits of information can be encoded, whichcould correspond with bits two and three 44, 46 of the lower modulationsub-symbol 48 and bits zero and one 40, 42 of the higher modulationsub-symbol 50. The sixteen constellation points include a first quadrantfirst higher point 78, a first quadrant second higher point 80, a firstquadrant third higher point 82, a first quadrant fourth higher point 84,a second quadrant first higher point 86, a second quadrant second higherpoint 88, a second quadrant third higher point 90, a second quadrantfourth higher point 92, a third quadrant first higher point 94, a thirdquadrant second higher point 96, a third quadrant third higher point 98,a third quadrant fourth higher point 100, a fourth quadrant first higherpoint 102, a fourth quadrant second higher point 104, a fourth quadrantthird higher point 106, and a fourth quadrant fourth higher point 108.

FIG. 6 shows the 4 constellation points used in the first quadrant 62 of16-QAM, which include the first quadrant points 78, 80, 82, 84. If thefour first quadrant points 78, 80, 82, 84 are used to represent 4different possible modulation points, then 2 bits of information can beencoded, which could correspond with bits zero and one 40, 42 of thehigher modulation sub-symbol 50. The first quadrant first higher point78 may be represented with bit zero 40 equal to a zero and bit one 42equal to a zero. The first quadrant second higher point 80 may berepresented with bit zero 40 equal to a one and bit one 42 equal to azero. The first quadrant third higher point 82 may be represented withbit zero 40 equal to a zero and bit one 42 equal to a one. The firstquadrant fourth higher point 84 may be represented with bit zero 40equal to a one and bit one 42 equal to a one. In one embodiment of thepresent invention, the phases and amplitudes separating the firstquadrant points 78, 80, 82, 84 from each other may be less than thephases and amplitudes separating the groups of first quadrant points 78,80, 82, 84, second quadrant points 86, 88, 90, 92, third quadrant points94, 96, 98, 100, and fourth quadrant points 102, 104, 106, 108 from eachother; therefore, the reliability of data provided with the lowermodulation sub-symbol 48, called lower modulation layer data, may begreater than that provided for the higher modulation sub-symbol 50,called higher modulation layer data, particularly with wirelesscommunications links with low signal margins. In wireless communicationslinks that operate with high signal margins most of the time, thedifference in the reliabilities may be indetectable; however, thereliabilities over time, called average reliabilities will showdifferences due to those situations that may occasionally produce lowsignal margins.

In an alternate embodiment of the present invention, the hierarchicalmodulation method includes sixty-four quadrature amplitude modulation(64-QAM), which uses 64 constellation points. With 64 different possiblemodulation points, six bits of information can be encoded. The six bitsof information may be associated with two, three, or more modulationlayers. Each of the modulation layers may be associated with one bit,two bits, three bits, or any combination thereof. Generally, the presentinvention may be used with any modulation method, encoding any number ofbits, and associating the encoded bits with any number of modulationlayers. The modulation layers may all be allocated to two or more usersin any combination. In an exemplary embodiment of the present invention,64-QAM is used to encode six bits of information. Two of the six bitsare associated with a first modulation layer. Another two of the sixbits are associated with a second modulation layer. The remaining two ofthe six bits are associated with a third modulation layer. The threemodulation layers may be used to transmit three different streams ofdata to three different user elements. Alternatively, the bits of any orall of the modulation layers may be divided to transmit one stream ofdata to one user element and a different stream of data to a differentuser element.

Broadcast data is data that is intended to be received by more than oneend user. Another frequently encountered term in communications ismulticast. The only difference between broadcast data and multicast datais that broadcast data is intended for more end users than multicastdata; however, since there is no accepted dividing line betweenmulticast data and broadcast data, in this specification the termbroadcast should be taken to mean broadcast, multicast, or both.Broadcast data may be audio, video, or both. Examples of broadcast datainclude video programs and audio programs. Broadcast data with nationalcontent may include network programs such as national newscasts ormovies. Broadcast data with regional content may include regionalnewscasts or statewide information programs. Broadcast data with localcontent may include weather or traffic information. Broadcast data withbasic content may include network channels or news channels. Broadcastdata with supplemental content may include special interest channels,such as a sports channel or an educational channel. Unicast data is datathat is intended to be received by one end user. Examples of unicastdata include voice unicast data, such as cellular phone calls, specificunicast data, such as email messages, short message services, audiounicast data, such as an on-demand audio program, and video unicastdata, such as an on-demand video program.

Broadcast data or unicast data may be transmitted using channels orsub-channels. A channel is a flow of information that contains all ofthe information associated with an information group, such as a videoprogram together with its associated audio channels and sub-titles.Sub-channels are used to divide a channel into multiple flows ofinformation for transmission over some medium, such as a cellularnetwork. The information group is reconstructed by combining thesub-channels. Sub-channels are commonly used when communicationschannels in a communications system have inadequate bandwidth to handlethe full bandwidth of the information being transmitted.

The present invention includes processing different information streamsusing different modulation layers. OFDM is a technique for distributingdata over a number of OFDM sub-carriers, which can be created by anumber of different methods, so long as each sub-carrier is orthogonalwith respect to other sub-carriers. In this context, orthogonal meanseach sub-carrier does not interfere with the other sub-carriers. TheOFDM data can be provided by using carriers at different frequencies,which is known as frequency division multiplexing (FDM) associated withfrequency division multiple access (FDMA), time multiplexing, which isknown as time division multiplexing (TDM) associated with time divisionmultiple access (TDMA), spatial multiplexing, which is a associated withmultiple input multiple output (MIMO) systems that have multipleantennas such that each antenna may have different information, or anycombination thereof. The present invention includes dividing modulationsymbols, called modulation division multiplexing (MDM) associated with anew access technique called modulation division multiple access (MDMA).Related to OFDM is single carrier frequency division multiplexing(SC-FDM). The present invention may be used to provide one or moresub-carriers in an OFDM or SC-FDM system. Additionally, the presentinvention may be used with numerous multiplexing techniques, includingFDM, TDM, special multiplexing, MDM, OFDM, SC-FDM, or any combinationthereof.

In one embodiment of the present invention, the modulation sub-symbols48, 50 may include different types of information selected from thefollowing group, including video broadcast channels, video broadcastsub-channels, video unicast channels, video unicast sub-channels, audiobroadcast channels, audio broadcast sub-channels, audio unicastchannels, audio unicast sub-channels, voice unicast data, specificunicast data, OFDM data, and OFDM sub-carriers. Other embodiments of thepresent invention may include more than two different modulation layers.

In one embodiment of the present invention, the lower modulationsub-symbol 48 includes broadcast data having national content, and thehigher modulation sub-symbol 50 includes broadcast data having localcontent. In an alternate embodiment of the present invention, the lowermodulation sub-symbol 48 includes broadcast data having basic content,and the higher modulation sub-symbol 50 includes broadcast data havingsupplemental content. In an additional embodiment of the presentinvention, the lower modulation sub-symbol 48 includes informationintended to be directly received by a user element (UE). The highermodulation sub-symbol 50 includes information intended to be received bya relay station for forwarding to other relay stations, UE, or both. Abase station may serve as a relay station. A synchronization signal maybe included to synchronize transmissions to UE from multiple basestations or relay stations. The information included in the lowermodulation sub-symbol 48 may be repeated in the higher modulationsub-symbol 50. The synchronization signal may include a preamble tofacilitate synchronization.

The present invention includes processing different information streamsusing different modulation layers. Such processing may include providinga single frequency network (SFN). An SFN may be formed when multipleantennas in an RF communications system 10 transmit the same informationon the same modulation layer at the same time, which provides robustdata transmission since the multiple signals may fill in coverage holescaused by shadowing and multi-path effects; therefore, higher broadcastdata rates may be feasible with SFN. SFN data may be included in thelower modulation sub-symbol 48, the higher modulation sub-symbol 50, orboth. Some or all of the broadcast data that incorporates the presentinvention may include SFN data.

The present invention employs hierarchical modulation to simultaneouslytransmit information on different modulation layers using a carrier RFsignal. In one embodiment of the present invention, first data to betransmitted is assigned to a first modulation layer and second data isassigned to a second modulation layer based on reliability criteria. Thefirst and second modulation layers are hierarchical modulation layers ofthe carrier RF signal. Once assigned, the first data is transmittedusing the first modulation layer of the carrier RF signal and the seconddata is transmitted using the second modulation layer of the carrier RFsignal. One modulation layer is generally a higher order than the othermodulation layer.

In one embodiment of the present invention, all things being equal, thelower order modulation layer is generally more reliable than the higherorder modulation layer. In general, the reliability criteria takes thereliability characteristics of the different modulation layers intoaccount when assigning the first and second data to the differentmodulation layers. For example, reliability information may be derivedfrom signal strength measurements or channel conditions to determine anappropriate modulation to use for transmitting certain data.Alternatively, different data may be associated with differenttransmission priorities. An example of reliability criteria related totransmission of the data is data that cannot be re-transmitted requireshigher reliability than data that can be re-transmitted. Althoughmaintaining data integrity is important for file transfers, the relativetransmission priority for a file transfer is generally much lower thanthat for voice or other streaming media. In essence, the reliabilitycriteria may relate to the communication channels, the transmission ofthe data, or both. For the various data, the reliability information isused to assign the various data to the different modulation layers fortransmission.

In certain embodiments of the present invention, different data isbroadcast to multiple users using different modulation layers. Thedifferent data is assigned to specific modulation layers based onreliability criteria. In one embodiment of the present invention, asingle program is broken into two different data streams. One providesbasic resolution content while the other provides optional higherresolution content. Upon receipt of the lower resolution content, onlythe lower resolution version of the program is available. If the higherresolution content is available, the lower and higher resolutionversions of the program are combined to form a composite program of highresolution. With the present invention, the higher resolution content istransmitted using the lower order modulation layers and the lowerresolution content is transmitted using the higher order modulationlayers.

In voice applications, each modulation layer may support one or morevoice calls. As such, the reliability criteria is used when assigningdata for different voice calls to the different modulation layers. Somecalls are supported on higher order modulation layers while others aresupported on lower order modulation layers in light of the reliabilitycriteria.

In one embodiment of the present invention, the base stations 12, 16both transmit required broadcast data using the modulation layer withgreater reliability, and transmit optional broadcast data using themodulation layer with lesser reliability. In an alternate embodiment ofthe present invention, the base stations 12, 16 both transmit eithernational or regional data using the modulation layer with greaterreliability, wherein the first base station 12 transmits first localdata and the second base station 16 transmits second local data usingthe modulation layer with lesser reliability. In an additionalembodiment of the present invention, the base stations 12, 16 bothtransmit nominal resolution broadcast data using the modulation layerwith greater reliability, and transmit enhanced resolution broadcastdata using the modulation layer with lesser reliability. In an alternateembodiment of the present invention, the base stations 12, 16 bothtransmit basic programming data using the modulation layer with greaterreliability, and transmit supplemental programming data using themodulation layer with lesser reliability. In yet another embodiment ofthe present invention, the base stations 12, 16 both may transmitbroadcast video data. In an alternate embodiment of the presentinvention, the base stations 12, 16 may both transmit broadcast audiodata.

In one embodiment of the present invention, the higher modulation layerdata may include RF communications system control channel data. The basestations 12, 16 may both transmit broadcast data using lower modulationsub-symbols 48, and the first base station 12 may transmit unicast datadirected to the first mobile terminal 20 using higher modulationsub-symbols 50. In an alternate embodiment of the present invention, thesecond base station 16 may transmit unicast data directed to the secondmobile terminal 28 using one of the modulation sub-symbols 48, 50, andtransmit unicast data directed to the third mobile terminal 32 using theother of the modulation sub-symbols 48, 50. The modulation layer withgreater reliability is used with the data link with the lower signalmargin, and the modulation layer with lower reliability is used with thedata link with the greater signal margin.

The present invention includes transmitting different information usingdifferent modulation layers. Different embodiments will allocate thedifferent information to the different modulation layers in differentways. Those skilled in the art will understand the concepts of theinvention and will recognize applications of these concepts beyond thespecific examples given. It should be understood that these concepts andapplications fall within the scope of the disclosure and theaccompanying claims. Specifically, the different information may beassociated with any of the different modulation layers in any order. Thepresent invention may use two, three, four, or more modulation layers.The different information may be intended for two or more end usersassociated with two or more user elements. The different information maybe associated with the modulation layers in any combination.

FIG. 7A shows the alignment of lower modulation layer data 110 withhigher modulation layer data 112 in one embodiment of the presentinvention. The lower modulation layer data 110 includes a first lowerlayer sample 114, a second lower layer sample 116, a third lower layersample 118, and a fourth lower layer sample 120. The higher modulationlayer data 112 includes a first higher layer sample 122, a second higherlayer sample 124, a third higher layer sample 126, and a fourth higherlayer sample 128. The lower layer samples 114, 116, 118, 120 are timealigned with the higher layer samples 122, 124, 126, 128. In mixing asystem with phase and amplitude modulation, such as QAM, with a systemhaving only phase modulation, such as QPSK, the constellation points ofthe QAM system may not directly align with the constellation points ofthe QPSK system; therefore, time-shifting the lower modulation layerdata 110 from the higher modulation layer data 112 may improve signalmargins. In an alternate embodiment of the present invention, the lowermodulation layer data 110 is time-shifted from the higher modulationlayer data 112 as illustrated in FIG. 7B. The higher layer samples 122,124, 126 are time-shifted from the lower layer samples 114, 116, 118,120, which may help average the higher layer samples 122, 124, 126 tomake the lower layer samples 114, 116, 118, 120 line up closer tonominal constellation points of the QPSK system. A lower modulation ratefor the lower modulation layer data 110 may further improve the impactof averaging. Even though the lower modulation layer data 110 istime-shifted from the higher modulation layer data 112, which means thelower modulation sub-symbol 48 is time-shifted from the highermodulation sub-symbol 50, both modulation sub-symbols 48, 50 fall withinone modulation symbol period and are effectively transmittedsimultaneously.

FIG. 8A shows time multiplexed or TDM data included in the highermodulation layer data 112. The higher modulation layer data 112 includesa first sample of first time multiplexed data 130, a first sample ofsecond time multiplexed data 132, a second sample of first timemultiplexed data 134, and a second sample of second time multiplexeddata 136. The samples 130, 134 of the first time multiplexed data areinterspersed with the samples 132, 136 of the second time multiplexeddata. Different channels, sub-channels, or unrelated data streams may beincluded in the higher modulation layer data 112. Other embodiments ofthe present invention may include TDM data in the higher modulationlayer data 112, the lower modulation layer data 110, or both. Thepresent invention may use two, three, four, or more modulation layers.TDM data may be associated with any or all of the modulation layers. TheTDM data may be intended for one, two, three, or more user elements.

FIG. 8B shows two single-carrier orthogonal frequency divisionmultiplexing (OFDM) sub-carriers included in the higher modulation layerdata 112. The higher modulation layer data 112 includes a first sampleof a first OFDM sub-carrier 138, a first sample of a second OFDMsub-carrier 140, a second sample of the first OFDM sub-carrier 142, anda second sample of the second OFDM sub-carrier 144. The samples 138, 142of the first OFDM sub-carrier are interspersed with the samples 140, 144of the second OFDM sub-carrier. Other embodiments of the presentinvention may include OFDM data in the higher modulation layer data 112,the lower modulation layer data 110, or both.

FIG. 9 adds MIMO antennas to the base stations and some of the terminalsillustrated in FIG. 1. The first base station 12 includes a secondantenna port ANT2 coupled to a first MIMO base station antenna 146. Thesecond base station 16 includes a second antenna port ANT2 coupled to asecond MIMO base station antenna 148. The first mobile terminal 20includes a second antenna port ANT2 coupled to a first MIMO mobileterminal antenna 150. The fixed terminal 24 includes a second antennaport ANT2 coupled to a fixed MIMO antenna 152. The third mobile terminal32 includes a second antenna port ANT2 coupled to a second MIMO mobileterminal antenna 154. The second mobile terminal 28 does not have a MIMOantenna. The RF communications system 10 illustrated in FIG. 9 mayrepresent a communications system that has been upgraded to include MIMOcapability. The second mobile terminal 28 does not have MIMO capabilityand may represent a previous generation UE, or may be a low cost,reduced functionality UE sold for use in the MIMO RF communicationssystem 10. By using the present invention, the second mobile terminal 28may be able to transmit and receive lower modulation layer data 110 toand from the base stations 12, 16, and the other terminals 20, 24, 32may be able to transmit and receive both modulation layer data 110, 112to and from the base stations 12, 16.

The present invention includes processing different information streamsusing different modulation layers, such as MIMO. MIMO systems usemultiple antennas for each base station or terminal. The multipleantennas may provide spatial diversity, which allows spatialmultiplexing. Spatial multiplexing may allow different information to betransmitted and received from each of the multiple antennas. Othersystems may use multiple antennas for diversity. Data from singleantenna systems, such as the RF communications system 10 illustrated inFIG. 1 is known as single input single output (SISO) data. Data frommultiple antenna systems that has different information associated witheach antenna, such as the RF communications system 10 illustrated inFIG. 9 is known as MIMO data. By using SISO data with the lowermodulation layer data 110 and MIMO data with the higher modulation layerdata 112, the RF communications system 10 may be backward compatible bysupporting previous generation communications protocols and presentcommunications protocols.

FIG. 10 shows SISO data included in the lower modulation layer data 110,and two MIMO sub-channels included in the higher modulation layer data112. The lower modulation layer data 110 includes a first SISO datasample 156, a second SISO data sample 158, a third SISO data sample 160,and a fourth SISO data sample 162. The higher modulation layer data 112includes a first sample of a first MIMO sub-channel 164, a first sampleof a second MIMO sub-channel 166, a second sample of the first MIMOsub-channel 168, and a second sample of the second MIMO sub-channel 170.The samples 164, 168 of the first MIMO sub-channel are interspersed withthe samples 166, 170 of the second MIMO sub-channel. Other embodimentsof the present invention may include MIMO data in the higher modulationlayer data 112, the lower modulation layer data 110, or both.

FIG. 11 shows one embodiment of the present invention used with MIMOtransmitter circuitry 172. First transmit circuitry 174 receives bothlower modulation layer data LML and first higher modulation layer dataHML₁. The first transmit circuitry 174 provides a first modulated RFsignal to a first power amplifier 176, which provides an amplified firstmodulated RF signal to the first antenna port ANT1. The first modulatedRF signal is based on both the lower modulation layer data LML and thefirst higher modulation layer data HML₁. Second transmit circuitry 178receives both the lower modulation layer data LML and second highermodulation layer data HML₂. The second transmit circuitry 178 provides asecond modulated RF signal to a second power amplifier 180, whichprovides an amplified second modulated RF signal to the second antennaport ANT2. The second modulated RF signal is based on both the lowermodulation layer data LML and the second higher modulation layer dataHML₂. The lower modulation layer data LML is sent to both antenna portsANT1, ANT2. The first higher modulation layer data HML₁ is sent to onlythe first antenna port ANT1. The second higher modulation layer dataHML₂ is sent to only the second antenna port ANT2. In one embodiment ofthe present invention, the lower modulation layer data LML includesbasic broadcast data, the first higher modulation layer data HML₁includes first supplemental data, and the second higher modulation layerdata HML₂ includes second supplemental data. The second mobile terminal28 may receive the basic broadcast data, and the other terminals 20, 24,32 may receive the basic broadcast data, the first supplemental data,and the second supplemental data. All of the modulation layer data LML,HML₁, HML₂ is transmitted simultaneously. Each of the first and secondhigher modulation layer data HML₁, HML₂ is a MIMO sub-channel. The RFcommunications system 10 may have multiple base stations such that eachbase station has multiple antennas providing MIMO capability. All of thebase stations and antennas may be used to form an SFN using the samelower modulation layer data LML. The first and second higher modulationlayer data HML₁, HML₂ may be transmitted from different base stations,or an antenna on one base station may transmit the first highermodulation layer data HML₁ and an antenna on a different base stationmay transmit the second higher modulation layer data HML₂.

FIG. 12 shows details of the first base station 12 illustrated inFIG. 1. The basic architecture of the first base station 12 may includea receiver front end 182, a radio frequency transmitter section 184, anantenna 186, a duplexer or switch 188, a baseband processor 190, acontrol system 192, and a frequency synthesizer 194. The receiver frontend 182 receives information bearing radio frequency signals from one ormore remote transmitters provided by other base stations, terminals, orother user element. A low noise amplifier (LNA) 196 amplifies thesignal. A filter circuit 198 minimizes broadband interference in thereceived signal, while down conversion and digitization circuitry 200down converts the filtered, received signal to an intermediate orbaseband frequency signal, which is then digitized into one or moredigital streams. The receiver front end 182 typically uses one or moremixing frequencies generated by the frequency synthesizer 194. Thebaseband processor 190 processes the digitized received signal toextract the information or data bits conveyed in the received signal.This processing typically comprises demodulation, decoding, and errorcorrection operations. As such, the baseband processor 190 is generallyimplemented in one or more digital signal processors (DSPs).

On the transmit side, the baseband processor 190 receives digitizeddata, which may represent voice, data, or control information, from thecontrol system 192, which it encodes for transmission. The encoded datais output to the transmitter 184, where it is used by a modulator 202 tomodulate a carrier signal that is at a desired transmit frequency. Poweramplifier circuitry 204 amplifies the modulated carrier signal to alevel appropriate for transmission, and delivers the amplified andmodulated carrier signal to the antenna 186 through the duplexer orswitch 188.

The following description provides an overview of a wirelesscommunication environment and the architecture of a base station, orlike access point, and a mobile terminal, which may be used in an OFDMand MIMO environment.

With reference to FIG. 13, a base station controller (BSC) 206 controlswireless communications within multiple cells 208, which are served bycorresponding base stations (BS) 210. In general, each base station 210facilitates communications using OFDM with mobile terminals 212, whichare within the cell 208 associated with the corresponding base station210. The movement of the mobile terminals 212 in relation to the basestations 210 results in significant fluctuation in channel conditions.As illustrated, the base stations 210 and mobile terminals 212 mayinclude multiple antennas to provide spatial diversity forcommunications.

A high level overview of the mobile terminals 212 and base stations 210of the present invention is provided prior to delving into structuraland functional details. With reference to FIG. 14, a base station 210configured according to one embodiment of the present invention isillustrated. The base station 210 generally includes a control system214, a baseband processor 216, transmit circuitry 218, receive circuitry220, multiple antennas 222, and a network interface 224. The receivecircuitry 220 receives radio frequency signals bearing information fromone or more remote transmitters provided by mobile terminals 212(illustrated in FIG. 15). Preferably, a low noise amplifier and a filter(not shown) cooperate to amplify and remove broadband interference fromthe signal for processing. Downconversion and digitization circuitry(not shown) will then downconvert the filtered, received signal to anintermediate or baseband frequency signal, which is then digitized intoone or more digital streams.

The baseband processor 216 processes the digitized received signal toextract the information or data bits conveyed in the received signal.This processing typically comprises demodulation, decoding, and errorcorrection operations. As such, the baseband processor 216 is generallyimplemented in one or more digital signal processors (DSPs) orapplication-specific integrated circuits (ASICs). The receivedinformation is then sent across a wireless network via the networkinterface 224 or transmitted to another mobile terminal 212 serviced bythe base station 210.

On the transmit side, the baseband processor 216 receives digitizeddata, which may represent voice, data, or control information, from thenetwork interface 224 under the control of the control system 214, andencodes the data for transmission. The encoded data is output to thetransmit circuitry 218, where it is modulated by a carrier signal havinga desired transmit frequency or frequencies. A power amplifier (notshown) will amplify the modulated carrier signal to a level appropriatefor transmission, and deliver the modulated carrier signal to theantennas 222 through a matching network (not shown). Modulation andprocessing details are described in greater detail below.

With reference to FIG. 15, a mobile terminal 212 configured according toone embodiment of the present invention is illustrated. Similarly to thebase station 210, the mobile terminal 212 will include a control system226, a baseband processor 228, transmit circuitry 230, receive circuitry232, multiple antennas 234, and user interface circuitry 236. Thereceive circuitry 232 receives radio frequency signals bearinginformation from one or more base stations 210. Preferably, a low noiseamplifier and a filter (not shown) cooperate to amplify and removebroadband interference from the signal for processing. Downconversionand digitization circuitry (not shown) will then downconvert thefiltered, received signal to an intermediate or baseband frequencysignal, which is then digitized into one or more digital streams.

The baseband processor 228 processes the digitized received signal toextract the information or data bits conveyed in the received signal.This processing typically comprises demodulation, decoding, and errorcorrection operations, as will be discussed on greater detail below. Thebaseband processor 228 is generally implemented in one or more digitalsignal processors (DSPs) and application specific integrated circuits(ASICs).

For transmission, the baseband processor 228 receives digitized data,which may represent voice, data, or control information, from thecontrol system 226, which it encodes for transmission. The encoded datais output to the transmit circuitry 230, where it is used by a modulatorto modulate a carrier signal that is at a desired transmit frequency orfrequencies. A power amplifier (not shown) will amplify the modulatedcarrier signal to a level appropriate for transmission, and deliver themodulated carrier signal to the antennas 234 through a matching network(not shown). Various modulation and processing techniques available tothose skilled in the art are applicable to the present invention.

In OFDM modulation, the transmission band is divided into multiple,orthogonal carrier waves. Each carrier wave is modulated according tothe digital data to be transmitted. Because OFDM divides thetransmission band into multiple carriers, the bandwidth per carrierdecreases and the modulation time per carrier increases. Since themultiple carriers are transmitted in parallel, the transmission rate forthe digital data, or symbols, on any given carrier is lower than when asingle carrier is used.

OFDM modulation may require the performance of an Inverse Fast FourierTransform (IFFT) on the information to be transmitted. For demodulation,the performance of a Fast Fourier Transform (FFT) on the received signalis required to recover the transmitted information. In practice, theIFFT and FFT are provided by digital signal processing carrying out anInverse Discrete Fourier Transform (IDFT) and Discrete Fourier Transform(DFT), respectively. Accordingly, the characterizing feature of OFDMmodulation is that orthogonal carrier waves are generated for multiplebands within a transmission channel. The modulated signals are digitalsignals having a relatively low transmission rate and capable of stayingwithin their respective bands. The individual carrier waves are notmodulated directly by the digital signals. Instead, all carrier wavesare modulated at once by IFFT processing.

In one embodiment, OFDM is used for at least the downlink transmissionfrom the base stations 210 to the mobile terminals 212. Each basestation 210 is equipped with n transmit antennas 222, and each mobileterminal 212 is equipped with m receive antennas 234. Notably, therespective antennas can be used for reception and transmission usingappropriate duplexers or switches and are so labeled only for clarity.

With reference to FIG. 16, a logical OFDM transmission architecture isprovided according to one embodiment. Initially, the base stationcontroller 206 may send channel quality indicator (CQI) informationbased on carrier-to-interference ratios (CIR) to the base station 210.Additionally, the base station controller 206 will send data to betransmitted to various mobile terminals 212 to the base station 210. Thebase station 210 may use the CQIs associated with the mobile terminalsto schedule the data for transmission as well as select appropriatecoding and modulation for transmitting the scheduled data. The CQIs maybe directly from the mobile terminals 212 or determined at the basestation 210 based on information provided by the mobile terminals 212.In either case, the CQI for each mobile terminal 212 is a function ofthe degree to which the channel amplitude (or response) varies acrossthe OFDM frequency band.

Scheduled data 238, which is a stream of bits, is scrambled in a mannerreducing the peak-to-average power ratio associated with the data usingdata scrambling logic 240. A cyclic redundancy check (CRC) for thescrambled data is determined and appended to the scrambled data usingCRC adding logic 242. Next, channel coding is performed using channelencoder logic 244 to effectively add redundancy to the data tofacilitate recovery and error correction at the mobile terminal 212.Again, the channel coding for a particular mobile terminal 212 is basedon the CQI. The channel encoder logic 244 uses known Turbo encodingtechniques in one embodiment. The encoded data is then processed by ratematching logic 246 to compensate for the data expansion associated withencoding.

Bit interleaver logic 248 systematically reorders the bits in theencoded data to minimize the loss of consecutive data bits. Theresultant data bits are systematically mapped into corresponding symbolsdepending on the chosen baseband modulation by mapping logic 250.Preferably, Quadrature Amplitude Modulation (QAM) or Quadrature PhaseShift Key (QPSK) modulation is used. The degree of modulation ispreferably chosen based on the CQI for the particular mobile terminal.The symbols may be systematically reordered to further bolster theimmunity of the transmitted signal to periodic data loss caused byfrequency selective fading using symbol interleaver logic 252.

At this point, groups of bits have been mapped into symbols representinglocations in an amplitude and phase constellation. When spatialdiversity is desired, blocks of symbols are then processed by space-timeblock code (STC) encoder logic 254, which modifies the symbols in afashion making the transmitted signals more resistant to interferenceand more readily decoded at a mobile terminal 212. The STC encoder logic254 will process the incoming symbols and provide n outputscorresponding to the number of transmit antennas 222 for the basestation 210. The control system 214 and/or baseband processor 216 willprovide a mapping control signal to control STC encoding. At this point,assume the symbols for the n outputs are representative of the data tobe transmitted and capable of being recovered by the mobile terminal212. See A. F. Naguib, N. Seshadri, and A. R. Calderbank, “Applicationsof space-time codes and interference suppression for high capacity andhigh data rate wireless systems,” Thirty-Second Asilomar Conference onSignals, Systems & Computers, Volume 2, pp. 1803-1810, 1998, which isincorporated herein by reference in its entirety.

For the present example, assume the base station 210 has two antennas222 (n=2) and the STC encoder logic 254 provides two output streams ofsymbols. Accordingly, each of the symbol streams output by the STCencoder logic 254 is sent to a corresponding IFFT processor 256,illustrated separately for ease of understanding. Those skilled in theart will recognize that one or more processors may be used to providesuch digital signal processing, alone or in combination with otherprocessing described herein. The IFFT processors 256 will preferablyoperate on the respective symbols to provide an inverse FourierTransform. The output of the IFFT processors 256 provides symbols in thetime domain. The time domain symbols are grouped into frames, which areassociated with a prefix by like insertion logic 258. Each of theresultant signals is up-converted in the digital domain to anintermediate frequency and converted to an analog signal via thecorresponding digital up-conversion (DUO) and digital-to-analog (D/A)conversion circuitry 260. The resultant (analog) signals are thensimultaneously modulated at the desired RF frequency, amplified, andtransmitted via the RF circuitry 262 and antennas 222. Notably, pilotsignals known by the intended mobile terminal 212 are scattered amongthe sub-carriers. The mobile terminal 212, which is discussed in detailbelow, will use the pilot signals for channel estimation.

Reference is now made to FIG. 17 to illustrate reception of thetransmitted signals by a mobile terminal 212. Upon arrival of thetransmitted signals at each of the antennas 234 of the mobile terminal212, the respective signals are demodulated and amplified bycorresponding RF circuitry 264. For the sake of conciseness and clarity,only one of the two receive paths is described and illustrated indetail. Analog-to-digital (ND) converter and down-conversion circuitry266 digitizes and downconverts the analog signal for digital processing.The resultant digitized signal may be used by automatic gain controlcircuitry (AGC) 268 to control the gain of the amplifiers in the RFcircuitry 264 based on the received signal level.

Initially, the digitized signal is provided to synchronization logic270, which includes coarse synchronization logic 272, finesynchronization logic 274, and frequency offset and clock estimationlogic 276. The coarse synchronization logic 272 buffers several OFDMsymbols and calculates an auto-correlation between the two successiveOFDM symbols. A resultant time index corresponding to the maximum of thecorrelation result determines a fine synchronization search window,which is used by fine synchronization logic 274 to determine a preciseframing starting position based on the headers. The output of the finesynchronization logic 274 facilitates frame acquisition by framealignment logic 278. Proper framing alignment is important so thatsubsequent FFT processing provides an accurate conversion from the timeto the frequency domain. The fine synchronization algorithm is based onthe correlation between the received pilot signals carried by theheaders and a local copy of the known pilot data. Once frame alignmentacquisition occurs, the prefix of the OFDM symbol is removed with prefixremoval logic 280 and resultant samples are sent to frequency offsetcorrection logic 282, which compensates for the system frequency offsetcaused by the unmatched local oscillators in the transmitter and thereceiver. The synchronization logic 270 may include the frequency offsetand clock estimation logic 276, which is based on the headers to helpestimate such effects on the transmitted signal and provide thoseestimations to the correction logic 282 to properly process OFDMsymbols.

At this point, the OFDM symbols in the time domain are ready forconversion to the frequency domain using FFT processing logic 284. Theresults are frequency domain symbols, which are sent to processing logic286. The processing logic 286 extracts the scattered pilot signal usingscattered pilot extraction logic 288, determines a channel estimatebased on the extracted pilot signal using channel estimation logic 290,and provides channel responses for all sub-carriers using channelreconstruction logic 292. In order to determine a channel response foreach of the sub-carriers, the pilot signal is essentially multiple pilotsymbols that are scattered among the data symbols throughout the OFDMsub-carriers in a known pattern in both time and frequency. FIG. 18illustrates an exemplary scattering of pilot symbols among availablesub-carriers over a given time and frequency plot in an OFDMenvironment. Continuing with FIG. 17, the processing logic compares thereceived pilot symbols with the pilot symbols that are expected incertain sub-carriers at certain times to determine a channel responsefor the sub-carriers in which pilot symbols were transmitted. Theresults are interpolated to estimate a channel response for most, if notall, of the remaining sub-carriers for which pilot symbols were notprovided. The actual and interpolated channel responses are used toestimate an overall channel response, which includes the channelresponses for most, if not all, of the sub-carriers in the OFDM channel.

The frequency domain symbols and channel reconstruction information,which are derived from the channel responses for each receive path areprovided to an STC decoder 294, which provides STC decoding on bothreceived paths to recover the transmitted symbols. The channelreconstruction information provides equalization information to the STCdecoder 294 sufficient to remove the effects of the transmission channelwhen processing the respective frequency domain symbols

The recovered symbols are placed back in order using symbolde-interleaver logic 296, which corresponds to the symbol interleaverlogic 252 of the transmitter. The de-interleaved symbols are thendemodulated or de-mapped to a corresponding bitstream using de-mappinglogic 298. The bits are then de-interleaved using bit de-interleaverlogic 300, which corresponds to the bit interleaver logic 248 of thetransmitter architecture. The de-interleaved bits are then processed byrate de-matching logic 302 and presented to channel decoder logic 304 torecover the initially scrambled data and the CRC checksum. Accordingly,CRC logic 306 removes the CRC checksum, checks the scrambled data intraditional fashion, and provides it to the de-scrambling logic 308 forde-scrambling using the known base station de-scrambling code to recoverthe originally transmitted data 310.

In parallel to recovering the data 310, a CQI, or at least informationsufficient to create a CQI at the base station 210, is determined andtransmitted to the base station 14. As noted above, the CQI in apreferred embodiment is a function of the carrier-to-interference ratio(CIR), as well as the degree to which the channel response varies acrossthe various sub-carriers in the OFDM frequency band. For thisembodiment, the channel gain for each sub-carrier in the OFDM frequencyband being used to transmit information are compared relative to oneanother to determine the degree to which the channel gain varies acrossthe OFDM frequency band. Although numerous techniques are available tomeasure the degree of variation, one technique is to calculate thestandard deviation of the channel gain for each sub-carrier throughoutthe OFDM frequency band being used to transmit data.

Continuing with FIG. 17, a relative variation measure may be determinedby providing the channel response information from the channelestimation function 290 to a channel variation analysis function 312,which will determine the variation and channel response for each of thesub-carriers in the OFDM frequency band, and if standard deviation isused, calculate the standard deviation associated with the frequencyresponse. As noted, channel gain is a preferred measure of the channelresponse for calculating a CQI 314. The channel gain may be quantifiedbased on a relative amplitude of the channel frequency response indecibels (dB), and as such, the amplitude of the channel frequencyresponse may be represented by H_(dB)(k), which is a function of asub-carrier index k, where k=1 . . . k_(MIN), . . . k_(MAX), . . .k_(FFT). Notably, k_(FFT) is the number of sub-carriers in the entireOFDM frequency band, and the sub-carriers k_(MIN) through k_(MAX)represent the sub-carriers within the OFDM frequency band that areactually used to transmit data. Typically, a range of sub-carriers ateither end of the range of sub-carriers are not used, in order tominimize interference with other transmissions. As such, the degree ofvariation of the amplitude of the channel response may be determinedonly for the range of sub-carriers being used to transmit data (k_(MIN)through k_(MAX)). The standard deviation of the channel response acrossthe usable range of sub-carriers is calculated as follows:

$\begin{matrix}{{{std}\sqrt{\frac{1}{N_{u} - 1}{\sum\limits_{k_{MIN}}^{k_{MAX}}\left( {{H_{d\; B}(k)} - {\overset{\_}{H}}_{d\; B}} \right)^{2}}}},} & {{Eq}.\mspace{14mu} 1}\end{matrix}$

where N_(u) is the number of usable sub-carriers, H_(dB)(k) is the logamplitude of the channel frequency response, and H _(db) is the mean ofthe log amplitude of the channel response across the usable range ofsub-carriers or a subset thereof.

In a multiple-input multiple-output (MIMO) system where there aremultiple transmit and multiple receive antennas 222, 234 each linkcorresponding to transmit/receive antenna pairs will have a unique CQI.An aggregate CQI, or set of aggregate CQIs, may be required for theoverall MIMO set of links. To determine the aggregate CQIs, the channelfrequency response and CIR for each transmit and receive antenna pair isdetermined.

For multiple receive antennas 234, the multiple channel frequencyresponses are combined, to provide for the diversity achieved from themultiple receive antennas 234. This combining is an averaging of thepower of the respective channel frequency responses across the OFDMfrequency band. The channel variation measure is then determined acrossthe combined channel frequency response. The CIR values for therespective multiple receive antennas 234 are combined by summing.

For multiple transmit antennas 222, the modification to the CQI willdepend on the particular space time coding technique employed to reflectthe method by which the transmit diversity is being achieved by the codeand used by the system. Some schemes, such as transmit diversity, willrequire that the respective channel frequency responses from themultiple transmit antennas 222 be combined as described for the multiplereceive antennas 234 by averaging the power of the channel frequencyresponses across the OFDM frequency band. The channel variation measureis made across the combined frequency response. Further, the CIR valuesfor the multiple transmit antennas 222 are also combined. For otherschemes, a separate CQI may be determined for each transmit antenna 222and relayed back to the base station 210. The base station 210 may usethe CQI per transmit antenna 222 to separately adapt the modulation andcoding on the data transmitted on the respective transmit antennas 222.

Those skilled in the art will recognize improvements and modificationsto the preferred embodiments of the present invention. All suchimprovements and modifications are considered within the scope of theconcepts disclosed herein and the claims that follow.

1. A method for transmitting information to at least one user elementfrom at least one communication interface comprising: receiving firstdata intended for transmission to a first receiver and second dataintended for transmission to a second receiver; and transmitting thefirst and second data using a plurality of modulation layers of acarrier radio frequency signal, wherein each modulation layer of theplurality of modulation layers is a hierarchical modulation layer of thecarrier radio frequency signal, and wherein said transmitting comprisestransmitting the first data to the first receiver using a firstmodulation layer of the plurality of modulation layers and transmittingthe second data to the second receiver using a second modulation layerof the plurality of modulation layers.
 2. The method of claim 1, whereinthe carrier radio frequency signal comprises a plurality of modulationsymbols, such that each of certain of the plurality of modulationsymbols comprises a plurality of bits that provides the plurality ofdata.
 3. The method of claim 1, wherein the carrier radio frequencysignal comprises a plurality of modulation symbols, such that each ofcertain of the plurality of modulation symbols comprises a plurality ofbits that provides the first and second data, and the plurality of bitscomprises at least one first order bit that provides the first data andat least one second order bit that provides the second data.
 4. Themethod of claim 3, wherein the at least one first order bit is of ahigher order than the at least one second order bit.
 5. The method ofclaim 3, wherein the certain of the plurality of modulation symbols arequadrature amplitude modulation symbols.
 6. The method of claim 5,wherein the quadrature amplitude modulation symbols are associated withsixteen or sixty-four quadrature amplitude modulation.
 7. The method ofclaim 1, wherein the first data is associated with a first cellulartelephone call and the second data is associated with a second cellulartelephone call.
 8. The method of claim 1, further comprising: assigningthe first data to the first modulation layer and the second data to thesecond modulation layer based on reliability criteria.
 9. The method ofclaim 8, wherein the reliability criteria comprises at least oneselected from a group consisting of signal strength, communicationschannel conditions, and priority of transfer of the first data and thesecond data.
 10. The method of claim 1, wherein said receiving comprisesreceiving third data for transmission to a third receiver, wherein saidtransmitting comprises transmitting the third data using a thirdmodulation layer.
 11. A system for transmitting information at a networkelement, the system comprising: transmission circuitry for performingwireless transmission; and processing hardware coupled to thetransmission circuitry, wherein the processing hardware is configuredto: receive first data intended for transmission to a first receiver andsecond data intended for transmission to a second receiver; and transmitthe first and second data using a plurality of modulation layers of acarrier radio frequency signal via the transmission circuitry, whereineach modulation layer of the plurality of modulation layers is ahierarchical modulation layer of the carrier radio frequency signal, andwherein said transmitting comprises transmitting the first data to thefirst receiver using a first modulation layer of the plurality ofmodulation layers and transmitting the second data to the secondreceiver using a second modulation layer of the plurality of modulationlayers.
 12. The system of claim 11, wherein the carrier radio frequencysignal comprises a plurality of modulation symbols, such that each ofcertain of the plurality of modulation symbols comprises a plurality ofbits that provides the plurality of data.
 13. The system of claim 11,wherein the carrier radio frequency signal comprises a plurality ofmodulation symbols, such that each of certain of the plurality ofmodulation symbols comprises a plurality of bits that provides the firstand second data, and the plurality of bits comprises at least one firstorder bit that provides the first data and at least one second order bitthat provides the second data.
 14. The system of claim 13, wherein theat least one first order bit is of a higher order than the at least onesecond order bit.
 15. The system of claim 13, wherein the certain of theplurality of modulation symbols are quadrature amplitude modulationsymbols.
 16. The system of claim 15, wherein the quadrature amplitudemodulation symbols are associated with sixteen or sixty-four quadratureamplitude modulation.
 17. The system of claim 11, wherein the first datais associated with a first cellular telephone call and the second datais associated with a second cellular telephone call.
 18. The system ofclaim 11, wherein the processing hardware is further configured to:assign the first data to the first modulation layer and the second datato the second modulation layer based on reliability criteria.
 19. Thesystem of claim 18, wherein the reliability criteria comprises at leastone selected from a group consisting of signal strength, communicationschannel conditions, and priority of transfer of the first data and thesecond data.
 20. The system of claim 11, wherein said receivingcomprises receiving third data for transmission to a third receiver,wherein said transmitting comprises transmitting the third data using athird modulation layer.